The present invention generally relates to cameras, and more particularly to a method and apparatus for measuring various performance time characteristics of a camera shutter apparatus. Proper operation and adjustment of the shutter apparatus of the camera is critical in obtaining the correct exposure conditions for the film. Insufficient, or improper, or non-uniform exposure of the film will result in poor photographs. After periods of prolonged use and possible rough handling, the performance characteristics of the shutter apparatus may change; consequently, it is the usual practice to check and readjust the shutter apparatus to obtain the desired performance characteristics.
Presently, a variety of different measuring devices for determining the shutter speeds and exposure times of cameras are known, but the known devices suffer from one or more deficiencies. The typical measuring device provides only one measurement of the exposure, usually in terms of a percentage of change from a desired amount. This single exposure measurement generally makes it difficult to adjust a shutter apparatus of the type having leading and trailing curtains which traverse a focal plane aperture. In such shutter apparatus the exposure time is determined by the width of a slit between the curtains and the speed in which the curtains traverse the aperture. If each curtain traverses the focal plane at a different speed, the exposure time from one point to another across the focal plane aperture changes, since the width of the slit between the curtain changes. Consequently, one objective in obtaining relatively uniform exposure time is to cause both curtains to traverse the focal plane aperture in approximately the same time or at the same speed. If the exposure time is improper, one or the other of the leading or trailing curtains must be adjusted, but without measurements of the actual times for the leading and trailing curtains to traverse the focal plane aperture, it is difficult to adjust the curtains properly.
Another problem with known measuring devices is the impossibility of determining the exposure conditions from one point to the next across the focal plane, usually at the beginning and at the end of the traverse. In some relatively sophisticated cameras, the exposure width is designed to be different at the beginning and at the end of the traverse to compensate for an acceleration or a rapid burst of speed of the curtains at the start of the traverse. The initial burst of speed of the curtains requires a wider slit between the curtains at the beginning of the traverse and a gradually narrower slit at the end to obtain uniform exposure at the focal plane. A compensation or braking device is typically used to vary the width of the exposure slit, by reducing the speed and narrowing the exposure width after the traverse starts, and measuring this change in exposure time is important in properly adjusting the compensation or braking device. Known measurement devices do not provide any indication in the change in exposure time.
Known measuring devices supply an indication of the degree of synchronization between a desired photoflash delay and the actual photoflash delay of a certain camera. The synchronization indication does not provide an actual measurement of the delay time period, which makes rapid adjustment of the camera's photoflash delay difficult.
It is a general object of the present invention to overcome the foregoing described deficiencies of known measurement devices for camera shutter apparatus, and to completely measure all relevant performance times associated with curtain type shutter apparatus. More directly, the objectives of the present invention involve obtaining accurate and complete measurements of the leading and trailing curtain traverse times, of an initial exposure time, of a photoflash delay time, and of a change in exposure time at the beginning and the end of the traverse of the curtains of the focal plane aperture. Other objectives of the invention relate to measuring the operational characteristics more completely and accurately for all types of shutter apparatus. Still other objectives of the invention relate to collecting complete data on the performance characteristics of the shutter apparatus from one operation of the shutter apparatus and retaining the data for repeated selection and display. Other features of the invention relate to various improvements in shutter performance measuring apparatus, including the use of relatively inexpensive electronic elements arranged for obtaining very accurate measurements and for direct display of the performance time characteristics measured.
In accordance with the present invention, the invention may generally be summarized as comprising various measuring means for measuring an elapsed time for the leading curtain to traverse the focal plane aperture, for measuring an elapsed time for the trailing curtain to traverse the focal plane aperture, and for measuring a time period between the time that the leading curtain starts the traverse and the time that the trailing curtain starts the traverse. A display means is operative for displaying the times measured. Also included are measuring means for measuring a time delay between the time that the leading curtain starts the traverse and the time of energization of a photoflash apparatus controlled by the camera, and measuring means for measuring a change in exposure time at the start and at the end of the traverse of the curtains. The apparatus of the present invention may include digital circuit elements, a clock for providing pulses at predetermined fractions of seconds to count the times measured, and a means for selecting certain of the times measured for display. The method of the present invention includes measuring the elapsed time for the leading curtain to traverse the focal plane aperture, measuring an elapsed time for the trailing curtain to traverse the focal plane aperture, and measuring an initial exposure time. The method may also include measuring a time delay for the energization of the photoflash apparatus and measuring a change in exposure time as the curtains traverse the focal plane aperture. The invention is also applicable to measuring performance characteristics of various shutter apparatus, including blade type shutter apparatus.
A more complete understanding of the invention, as well as other objectives and features may be obtained from the following detailed description of the invention and from the brief description of the drawing.